A joining device for joining substrates together includes a first holding member configured to vacuum-suck a first substrate to draw and hold the first substrate on a lower surface thereof, and a second holding member disposed below the first holding member and configured to vacuum-suck a second substrate to draw and hold the second substrate on an upper surface thereof. The second holding member includes a body portion formed into a size larger than the second substrate when seen in a plan view and configured to vacuum-suck the second substrate, a plurality of pins provided on the body portion and configured to make contact with a rear surface of the second substrate, and an outer wall portion annularly provided on the body portion at an outer side of the plurality of pins and configured to support an outer periphery portion of the rear surface of the second substrate.